THE DERIVED ALBUMINS. 61 



aration is obtained if to the saturated fluid is added a small amount 

 of acetic acid that has been saturated with the salt. 



Neutral or acid solutions of albumoses are not coagulated by heat 

 nor on treating with alcohol, although they are precipitated when 

 this is present in considerable concentration. After precipitation, 

 however, they are as soluble as before, and in this respect they differ 

 markedly from the albumins proper. 



Like the native albumins, the albumoses are precipitated by nitric 

 acid, potassium ferrocyanide and acetic acid, metaphosphoric acid, 

 phosphotungstic acid in the presence of hydrochloric acid, tannic 

 acid, picric acid, trichloracetic acid, etc. ; but it must be noted that 

 on the subsequent application of heat the precipitate redissolves, 

 but reappears on cooling. The same result is obtained by treating 

 a solution of albumoses with an equal volume of a saturated solution 

 of sodium chloride and acidifying with acetic acid. 



The Peptones. In conformity with Kiihne's teachings, the term 

 peptone has been used to designate those products of proteoly tic di- 

 gestion which can no longer be salted out with ammonium sulphate, 

 either in neutral, acid, or alkaline media, but which still give the 

 biuret reaction. Products of this order are formed both during 

 peptic and tryptic digestion. Those resulting in the former instance 

 were designated as amphopeptone on the assumption that in it the 

 hemi- and the anti- groups were still united, and it was sup- 

 posed that during tryptic digestion the hemi- group was further de- 

 composed, while the more resistent antipeptone remained as such. 

 More recent researches have materially modified this conception. 

 Kiihne's amphopeptone and antipeptone have now been definitely 

 proved to be no unities, and a hemipeptone as such is no longer 

 recognized. It has been shown that the differences between the end- 

 products of peptic and tryptic digestion are quantitative, rather than 

 qualitative, and that the term peptone comprises a number of hydro- 

 lytic decomposition-products which are essentially the same as those 

 which result from the albumins on hydrolysis with boiling mineral 

 acids and other means. Some of these bodies still give the biuret reac- 

 tion (the peptones proper), while this is absent in others (the peptids). 



Fischer's polypeptids which no longer give the reaction represent 

 molecular complexes in which several amino-acid radicles are still 

 united, and from which simpler peptids and free amino-acids may 

 result on further hydrolysis. On digestion with proteolytic ferments 

 (trypsin) products of this character are formed which energetically 

 resist further cleavage by the ferment, but which can be decom- 

 posed by boiling mineral acids with the liberation, in addition to small 

 amounts of alanin, leucin, aspartic acid, and glutaminic acid, of large 

 quantities of a-prolin, phenyl-alanin, and all the contained glycocoll. 



Siegfried's kyrins are probably analogous to Fischer's polypeptids. 



With the exception of a-prolin, phenyl-alanin, and glycocoll, the 

 remaining amino-acid radicles of the albuminous molecule are split 

 off as such during the process of digestion with more or less readi- 

 ness. In the case of tyrosin S7.6 of the total amount can already 



